Your understanding is incorrect.
I could be way off base here, but this is my understanding of the call.
It wasn't ruled a fumble, it was ruled a touchdown. The refs got together and confirmed that the ball crossed the goal line before he fumbled there fore it is a dead play and unreviewable to see if minnesota recovered the footbal, just the same as if he was ruled down by contact. However if they would have called it a fumble then whoever comes out of the pile with it has either a touchdown or a touchback. Thats why when Tice threw the red flag the ref told him he could not review the see if it was a fumble just to see if he crossed the goal line. Thats when he decided not to review it.
If it would have went the way some of you had described, that the ref would have said that the play was unreviewable, witch is not what he said, he said that "minnesota has decided not to review the play. Witch be the way we should have done anyway to show that it was not a touchdown. We wouldn't have gotten the ball, but it would have been 4th and 1 for the Packers.
I'm sorry that was so long! Dose this make sense?